1. Field of the Invention
The present invention relates generally to x-ray systems and devices. More particularly, exemplary embodiments of the invention concern systems and methods for using a set of two dimensional projection data to generate information that approximates x-ray behavior in a volume of interest so as to facilitate generation of tomographic images and development of diagnostic and treatment processes.
2. Related Technology
X-ray systems and devices are valuable tools that are used in a wide variety of applications, both industrial and medical. For example, such equipment is commonly used in areas such as diagnostic and therapeutic radiology. More particularly, the use of computerized tomography (“CT”) for medical imaging has resulted in many advances in medical imaging, as well as diagnostic and therapeutic radiology. With respect to these particular applications, tomographic imaging has advanced from conventional, or plain film, tomography to volumetric, or helical, computerized tomography.
In what is sometimes referred to as “classical” tomography, the x-ray source and the film, sometimes referred to as a “detector,” move simultaneously in opposite directions such that any line from the x-ray source to an arbitrary point on the film pivots about a fulcrum point. The motion is chosen such that the fulcrum points of lines from the source to the film surface collectively define a plane. Objects in the subject being imaged which lie close to this fulcrum, or focus plane, are in focus on the film, while objects not near this plane are blurred. This radiographic technique is also sometimes referred to as tomography, tomo, stratigraphy, and planography.
Many known tomographic processes and equipment involve the use of various numerical techniques and associated algorithms to generate and process the data necessary to radiographic procedures. For example, reconstruction algorithms based on the Radon transformation or extensions thereof are commonly employed to implement volumetric CT imaging. Other techniques sometimes employed include the algebraic reconstruction technique (“ART”), matrix inversion, and fast Fourier transform (“FFT”) techniques. Moreover, such algorithms are useful for application to a variety of physical system configurations. Examples of such physical configurations include rectilinear, fan beam, “fourth generation,” spiral, cone beam, multi-source, and two-dimensional detector arrangements.
While radiographic techniques such as classical tomography have proven useful and effective in many regards, problems with such techniques nonetheless remain. By way of example, practical x-ray beams, detectors and sources have finite attributes, such as their size. Moreover, the x-ray quanta are distributed in space and energy, or frequency. As well, classical tomography is prone to the presence of aliasing and other image artifacts in the generated tomographic images.
Yet another complication with typical systems and processes is that the individual detectors may have different x-ray detection efficiencies and/or nonlinear properties, depending on the intensity of the transmitted x-rays. Further, large portions of the detected x-ray intensity may be the result of scattered radiation. The detection of such scattered radiation degrades the quality, and thus the usefulness and reliability, of the generated images. Further, known systems and techniques are typically ineffectual in correcting for known systematic errors and x-ray attenuation line integrals which are optimum for the visualization. As a result, random errors often exceed acceptable limits.
In view of the foregoing, and other, problems in the art, what is needed are systems and methods configured to enable generation and accumulation of a sufficient quanta of two dimensional x-ray attenuation data such that the data has the accuracy and precision necessary to best produce the tomographic images required. Pre-processing should be applied to the data so as to correct for known systematic errors and x-ray attenuation line integrals which are optimum for the visualization. In addition, random error must be kept to an acceptable limit. Moreover, the accumulated x-ray attenuation data should reflect a set of different directions through each volume pixel, or voxel, of a volume of interest so that the voxel geometries and corresponding weights, which reflect x-ray attenuation in the respective voxels, can be used to optimize density and spatial resolution, while minimizing image artifacts, and thereby facilitate achievement of optimum visualization.